Manufacture of hollow panels



Sept. 16, 1952 M. PASQUIER 2,610,938

MANUFACTURE OF HOLLOW PANELS Filed Feb. 1, 1947 E MMJ/MM -7 rU A/E V5Patented Sept. 16, 1952 MANUFACTURE'OF HOLLOW PANELS Michel Pasquier,Portland, -reg., assignor. to M and M Wood Working. companmjPortland,Qreg, a corporation of Oregon" Application February 1, 1947,, Serialnmzazes reclaims. (01; 154-418),

This invention relates to a novel and improved method of and apparatus.for drying" and setting the glue in the manufacture of hollow core woodpanels. a

In the manufacture'of' hollow core wood panels with thermosetting gluesit has heretofore been the usual practice to place thehollow panelassemblies in a hot press similar to-a: plywood hot plate press,'andapply heat and pressure tothe exterior faces of the panels. in order toset the glue in the internaljoints. In this operation the hollow panelsare interspersed between 'a series of heated platens-in an hydraulic,press'ancl are forced together as in making. plywood. Heat is therebytransmitted from the hot platens through all parts of the face sheets'ofthe'panels meet the gluein the internal glue lineabetween the insidesurfaces of the face sheets-and't'he several longitudinal and.transverse frame members with which they arepressedrinto' firmcontact.

This method of setting the glue is. subject to several seriousdisadvantages- In the first place it will be readily apparent that agreat. amount of heat is wasted because substantially the entire woodcontent of the panel must. be heated in order to heat the glue line's.Moreover, thehighest temperature is produced on the outside surface ofeach face sheet with the glueline surface lying on the relatively coolside of the sheet whereby the outer surface must be :raised to atemperature higher than thatrequired to set the glue by an amountcorresponding to the" temperature gradient through. the sheet. Most ofthe heat which goes into the panels from the. heated platens istherefore wasted inraising the temperature of the outer portions of theface sheets" which are relatively poor conductors of heat. In order toreduce the temperature gradient' through the face sheets the time oftreatmentv must beprolonged, thereby proportionately reducing the outputof each hot press and; necessitating a larger plant investment in hotpresses for agiven output of the-product.

Another and very serious-objection to the application of hot'platens to'the outer panel surfaces is the checking of the panel surface-producedby the rapid d-rying action of thehightemperatures, the checking beingmore-severewhen the face sheets are thick, because of thehigher platentemperatures o'r'longer heating times required. The checking tendency'isaggravated by the usually high'moisture content of the plywood surfaceswhereby they are more'susceptible to checking than the'relatively dryveneers in the original: hotpressing operation in which the plywood waspreviously formed.

Hollow core panels have also beenglued' up with cold setting resing1ues',.us'ingiclampsto hold the panel assembliestogetherafter removalfrom the press. This procedure in'vo'lve'sra long clamp- 2 ing time andgreater glue. spreads in the absence of heat. 1 Also; in the absence. ofheat the glue is less water resistant. The clamps do not provide anabsolutely positive pressure to prevent warping, and there is alwaysdanger of the clamps beingv disturbed upon removal from the press.

The. generalobject of the present invention is, therefore, to provide animproved method of drying. and-setting the glue in hollow panels whichwill obviate. the objections anddisadvantages mentioned abovein order.to produce hollow wood panels of higher quality and more: economicallythan has heretofore been possible with conventional methods;- 7 V I 1Another object {is to provide a. novelmethod of heating and settingiithermosettingglue in hollow panel's. wherein the-heat is applieddirectly to the glue linev surfaces Where itisneeded sothat the finishedoutside surfaces may be maintained relatively cool inthe gluing andpressing, process, thereby to retain their normal physical properties. aI

A particular object issto provide a, method of heating the. interiorsurfaces which are to be glued by blowing a heating fluid: into thepanels.

Another object .is. to provide a'method of heating; hollow panelsinteriorlywhereby a thermosetting glue may be heat set me. cold pressinstead ofa-hotpress.

Another objectis. to'providea novel methodrof applying. heat-'togluedjoints.

Another object. is. to speed up the production ofihollow-core: panelsin: multiple quantitiesin cache press load, .and'to maintain a highproductionrate despite the use of plywood face sheetsofldifferentithickness.

Another object isutoprovide an apparatus for circulating a: heated fluidmedium through a load of hollow panels ina cold-press.

Witlrthese andother objects inview the invention resides in themethod-and apparatus which will be described with reference to apreferred embodiment-of the apparatus illustrated in the accompanyingdrawings.

Inthedrawings I Figure I is a vi'ew in side elevation showing apreferred form-'- of ;apparatus for carrying out". the method of theinvention;

Figure *2'is a top plan view of the apparatus shownin Figure ,1;

Figure 3 i's'a cross sectional view taken on the line 3-3 of Figure 1; fI I I Figure: 4 is an enlarged fragmentary view of one of thehotairpipes; and) Figure!) is a perspective view with parts broken away of' ahollow panelillustrating. a type of construction'to which the.invention. is applicable The apparatus shown generally liigures 1 to 3is' adapted to carry-out the method ofjthe invention in gluing astack-of hollow core-panels process upon opposite sides of a hollowframe-, work of longitudinal and transverse wood strips.

The face sheets I I are preferably plywood panels made by gluing threeor more Wood veneers together face to face in a previous operationwhereby the glue between the veneers is already set and the panels I Iare in a finished condition before assembling and gluing up'thecomposite hollow panel I0. The method of the present invention has itsmost advantageous application in connection with the use ofthermosetting resin types of glue wherein both the glue used in makingthe panels II and in gluing these panels to the hollow framework is athermosetting weather-resistant glue of the type ordinarily used formaking exterior grade plywood, but the method may also be practiced withthermoplastic and other conventional cold setting glues in order to savetime and space in the gluing-up process.

The framework for the panel I I! in the'present instance comprises apair of longitudinal strips I2 at the opposite side edges of the paneland one or more longitudinal strips I3 therebetween, depending upon thewidth of the panel. The ends of all these longitudinal strips are fittedby suitable joints into transverse end strips I4 at the ends of thepanel to provide a solid marginal framework upon which the sheets II maybe glued, and providing also intermediate supporting and spacing meansat each of the internal longitudinal members I3. This arrangement of theframe members I2, I3 and I4 forms a plurality of chambers I5 within thepanel containing the glue line surfaces to which glue is applied foruniting the face sheets with the internal framework. Thus, in gluing upthe panel III the edge strips I2 have opposite faces I6 and the endstrips I4 have opposite faces I! all lying in common planes and incontact with the inner surfaces of the respective face sheets 'I I.Similarly the intermediate strip or strips I3 have opposite faces I8lying in the same planes and in contact with the face sheets II. Theseface surfaces I6, I! and I8 constitute one side of the gluelinesurfa'ces between the frame. and the face sheets which hold thepanel together as an integral unit after the glue has set. In making upone of the hollow panels I glue is applied to these glue line surfacesand the different members are preferably temporarily held in place by afew small nails so that the panel may be -handled to loadit into thepress for drying the glue. V

In order to practice the method of the invention, the chambers I are notentirely sealed, but are provided with opposite end openings formed bynotches in the end strips I4. In making hollow panels for certainpurposes it is customary to provide aplurality of notches 20approximately in the positions shown to accommodate fastenings or otherfixtures, but if these notches are not required for such purposes,similar notches or holes should be cut in the end strips to communicatewith the interior of each chamber I5; Thus, if there is one centralstrip I3, there should be one notch or hole 20 in each end strip I4 oneither side ofthe centralstrip I3, and if there are more of these stripsa-notch or hole 20 should be provided at each endof each of the chambersI5., The holes or; notches can be plugged later if desired. 7

In practicing the method of the invention, hot air is blown interiorlythrough the panels so that it will come in direct contact with thesurfaces which form the glue lines I6, I! and I8 in order to provide adirect and short path from the heating medium to all parts of the glueline. In Figure 5 the arrows 2I indicate hot air blown in at one end ofthe panel, and the arrows 22 indicate the paths of hot air leaving thepanel, whereby hot air is pumped through the panel in sufficientquantity to heat the glue lines to the temperature required to set theglue. It is, of course, necessary to apply pressure over the face of thepanel to hold the face sheets and internal frame members in intimatepressure contact at their glue lines while the latter are being heatedin order to obtain a good bond, this being the function of the press.

Figures 1 to 3 disclose an economical apparatus for gluing up a stack ofhollow panels of the type described very quickly and with relativelysmall energy requirements in the press and in the heating system. Thenumeral 30 designates the base of a press which may be a conventionalcold press'of the type ordinarily used in making plywood with coldsetting glues. Beneath the base 30 are a plurality of hydrauliccylinders 3I having pistons 32 for raising and applying the necessaryupward pressure to a bottom platen 33 which is shown in Figure 1 inlowered position to receive a press load of the hollow panels I0. Thepanels in this press load have had a thermosetting glue applied to thesurfaces I5, I! and I8 and the face sheets have been nailed lightly tothe various frame members to hold the parts in place. A plurality ofposts of columns 34 extend upwardly from the base 30 to support a rigidtop platen 35 in a fixed position. After a press load of panels has beenplaced on the bottom platen 33, the latter is raised by the pistons 32to press the load against the top platen 35 in the usual manner as shownin Figure 3. Neither of these platens is heated, and when athermosetting glue is employed which sets in the press, intermediatecaul boards, platens and clamps are not used, the stack of panels Inconsisting solely of panels.

The press load is completely enclosed after it has been raised againstthe upper platen with sufficient force to apply the proper pressure overthe glue lines. The sides of the press are adapted to be closed bypanels 36 and 31, and if the press is loaded and unloaded from the sameside, one of these panels such as the panel 31 may be fastenedpermanently in place. In the present construction, the panel 36 isslidable in guides 36a so that it may be raised vertically by ropes 38or other lifting means but this panel may be hinged or mounted in anyother way to open and provide access for loading and unloading thepress. The ends of'the press are enclosed by funnel shaped hoods 39connected with the airoutlets of blowers 40 and 4 I.

Air is drawn into these blowers through heat exchangers 42 and 43 havingsteam pipes 44 or other heating elements therein, and the blowers aredriven by electric motors 45 wired in separate circuits forindividualoperation. Between the respective blowers and the hoods 39 arepipes 46 provided with angular discharge pipes 41 and 48. Suitable valvemeans are interposed between these discharge pipes and the pipes 46 sothat when one of the pipes 46 is blowing into the press the other willexhaust, and vice versa. In the present embodiment this valve meanscomprises the flap valves 50 and 5| which are hinged at 52 to fall bygravity to the positions shown when the blowers are not operating. Whenone of the blowers is started, theiair flow therefrom operates to raisethe adjacent flap valve to open the pipe 46 and close the entrance tothe discharge pipe on the air input side of thepress, the remoteflapvalve remaining down.

When the blower 4|] is operating, the'blower 41 is switched off, wherebythe air stream deliver'e'd from the blower 40 raises the flap valve- 50.toclose the discharge pipe 41 and open the pipe 46 to admit hot airthrough the hood 39 to the left endof the stack of panels lo, the latterthenbeing raised against the topplaten so that the lower platen 33 isapproximately on arlevel with the bottom of the hoods 39. Vertical stopsor partitions 53 are preferably provided between the ends of the pressload and the side panels 36 and 3| to prevent the air from theblowerfrom passingiaround the sides of the press load if the hoods 39 donot-snugly fit the-ends of .the'load. The partitions53 separate the endchambers defined principally by'hoodsv 39 from the side chambers whichare defined principally by the panels 36 and 31. Operation of. theblower 49 thereby produces sufficient pressure in the adjacent pipe 46and hood 39 to cause air to pass through the openings 20 and flowthrough the interior chambers l5 in each panel in the stack to applyheat directly to the inner surfaces of the. face sheets H to heat thevarious glue lines on these surfaces. Thus, air enters the panels asindicated by the arrows 2| in Figure 5 and leaves the panels asindicated by the arrows 22, afterwhich it is diverted by the loweredflap valve 5'! into the discharge pipe 48.

Heat transfer from the air stream to the interior surfaces of the panelslowers the temperature of the air as it travels through the panels tothereby establish a temperature gradient through the panels. In order toreducev the temperature difference in different parts of the panels, thepresent system is designed to reverse the air fiow from time to time tobring both ends of the panels up to substantially the same temperature.This is accomplished by merely switching off the blower 40 after a shortinterval of operation and switching on the blower 4|, which function maybe performed automatically by a time or temperature responsive switch.mechanism. The discharge from the blower 4| then raises the flap valve5| and reverses the direction of air circulation through the stack ofpanels. valve 5i! falls by gravity, if it is not already down, andconnects its hood 39 with the discharge pipe 41'. Hot air from theblower 4| is then blown into the cool ends of the panels and out of thepreviously heated ends until the end of the press load facing the blower4| becomeshotter than the" end facing the blower 40. The air flow maythus be reversed from time to time until the glue lines in the centersof the panels have been raised to a temperature sufiicient to set'theglue, at which time the operation is completed, and the blower thenoperating may be stopped and empress load removed from the press.

To conserve heat, the air maybe re-circulated by leading the dischargepipe 48 back to the inlet of heat exchanger 42 and blower -40,'andsimilarly leading the discharge pipe 41 back to the inlet of heatexchanger 43 and blower. 4|. In thereturn circulation of the air.provision should be made for removing moisture and. this When thisoccurs the 'fiap maybe accomplished by venting part. of the air toatmosphere and introducing some outside relatively. dry, air to take itsplace; I 4 Regardless of which waytheair is circul'atin'g at anyparticular instant, the heated air in'b'oth hoods 33 in. contactwithathe pa'nel ends heats the edge surfaces of the. strips ili iiandtheends of theiface sheets causing the h'eat to travel backthroughithe'glue line on the surfaces H. The, .hotair" within thechambers I5: heats this glue line from its other edge andcafuses heat-totravel into the joint, whereby half the width of the glue line is.heated from the outside and the other half is heated from the'zinsideof thepane1. Similarly, in the case of the glue line"surface |8 on thestrip or strips: l3, the heat: travels inwardly from-both. edgesexposedin the two chambers- I5- so as to heat the entire width of theglue line surface to thetemperature necessary; for settingthe glue. V 1

In'thei case of, the gluexline surfaces Son the marginal strips l2, thehot air in the chambersl5 causes heat to travel outwardly through theglue. line, -and if, these-surfaces ardrelativelynarrow and sufficienttime is allowedythe' heat applied from the inside will travel entirelyacross the glue line to heat all parts thereof to thextem peraturenecessary for setting the glue. I-Iow-. ever, it is preferred to applyheat externally-to the sides of the stack ofpanels to cause heat to alsotravel inwardly through these glue. lines in order; to reducev the timefactor and to reduce the temperature gradient which would have tobeestablished if the heat flow were entirelyin one direction through thejoint. I Varioustypes'of heating means such as infra-- red or otherradiant heaters may be .used to heat the sides ofthe stack of panels,but in. the pres ent apparatus it is preferred to utilize hot air fromthe heat exchangers 42 and 43. For this purpose pipes and 56are-1edoutof the hous ings of the blowers 4|! and 4| at'points of maximum pressuretherein to provide a good flow of hot air. The pipes 55 and connectwithheaders:5|' and 58-.which distribute the flow equally between a pairof pipes '60 mounted oneopposite sides of the top platen 35 just abovethe. top: of the pressload, asshown inFigure 3. The pipes 68 areprovided with a series of holes 6|on their under sides to direct hotairdownwardly alongthe sides of the press load as shown. This air isdischarged through openings 62 provided either in theside edges'ofthebottom platen: 33 or dbgtlween theplaten-and. the side panels135 an Iv "The hot .air supplied by the pipes the I spaces or. chambers betweenthe side-"panels 36' and 3 7Land the sides of the press load therebyheats-the outside surface of. each strip'-|'2.--and the edge ofeach'face sheet II to cause heat to travel inwardly across each igluelin'e' surface"|i6-1 in the samemanner that the. hot air in the hoods 39causes heat to travel inwardly across the glue line surfaces I! attheiends of the panels. The air discharged from the pipes is preferablyconfined'between the stops or partitions 53, orother' suitable headersat the ends of the press load, sothat this air circuit constitutesagseparate heating medium which ismaintained separate and distinct fromthe air circuitthrough' the hoods 39. In thisv way the air flow throughthe" interiors of the panels is. not short circuited be controlled toproduce optimum temperatures 7 at the exposed edgesof all the gluelines. It is, of course, understood that all of the air pipes andconduits are of sufficient size to carry a flow of airflwhich isadequateto produce the desired heating effect. Likewise theholesBl inpipes 60 are of suificientsize and in sufiicient number for theyintended purpose.

One way check valves 63. and 64 are provided in the ends of the pipes 60to close the open ends of these pipes and cause all the air to bedischarged through theholes 6|. The discharge of air from the blower 40causes the valves 63 to open and the valves 64 to close, and thedischarge of air from the blower 4| causes the valves 64 to open and thevalves 63 to close, somewhat in themanner of theflap valves 50 and 5!except that the valves 63 and 64 do not discharge air from the pipes.All the air introduced into the pipes 60 is discharged through the holes6| and exhausted from the press through the bottom openings 62, but thisair, also, may be recirculated if desired.

The apparatus for practicing the method of theinvention may employ onlya single blower and single heat exchanger provided with suitable pipingand valve arrangements to introduce the air flow alternately intoopposite ends of the panels, the side edges of the panels being heatedeither by separate pipes such as the pipes 60, by a return flow of theair which has passed through the panels, or by radiant heaters. It is atpresent preferred, however, to use two heat exchangers and two'blowersfor alternate operation in the general arrangement shown, although thearrangement of the apparatus and the details of construction are subjectto considerable modification as will occur to persons skilled in the artin practicing the method of the invention. It is also, of course,understood that suitable insulation should be provided on all the pipes,hoods, side panels and other exposed surfaces subjected to elevatedtemperatures in order to minimize the heat loss.

'For'the successful application of the method of the invention thechambers in the panels need not be entirely empty or devoid of fillingmaterial. It is often customary in panels of this type to insert someform of thermal insulation as a filler in the chambers l5 when thepanels are assembled, and several different forms of such insulatingmaterial are available which do not interfere with the internal heatingof the glue lines in the manner described. Certain common forms ofinsulation furnished in batts or strips to be tacked in place within thepanels offer substantially no impedance to the flow of air through thepanels and permit the'satisfactory heating of the glue line surfaces.Crinkled paper insulation, for instance, even though consider' ablystretched out and tacked in place to completely fill the length andwidth of each cham-' ber l5, exhibits a tendency to flutter in theinternal air stream and thereby provide equal access to the air for heattransfer to all the inside surfaces of the panel. The term hollow paneldoes not preclude the use of filling materials.

which permit an air flow through the panel. 7

' The great advantage of the present invention isthat the heat isapplied directly to the glue line surfaces so that it has a relativelyshort distance to travel along such surfaces to the innermost parts ofthe joint. The heat travel ,into the interior areas of the glue line isenhanced by the fact that the glue film is a relatively good conductorof heat in comparison withwood. When heat is applied to the panel facesin the conventional manner, as by heated platens and the like, to heatthe glue line surfaces l6, l1 and I8, a high temperature gradient mustbe produced through the thickness of the relatively non-conducting facesheets in order to heat a thermosetting glue to its criticaltemperature. Ordinarily, the heat from such a heated platen is appliedmore or less uniformly over the entire face of the panel whereby most ofthe heat is wasted in raising the mean temperature of the face sheetsconsiderably above the temperature attained in the glue lines. When theface sheets are thick, the high platen temperature necessary on theouter surface produces such severe cracking and checking that it becomesimpossible to produce a high grade product.

The method. of the present invention is economical of heat because theheat is not required to travel through the thickness of the face sheetsat a steep temperature gradient before it can perform its function ofsetting the glue. The glue line surfaces themselves attain the highesttemperature and the glue therein is set before there is an appreciableheating of the mass of the face sheets. When the face sheets arerelatively thick, their surfaces remain substantially unheated andtherefore undamaged by checking. The panel production rate is thereforeessentially the same for any thickness of face sheet, and if desired theface sheets may be of different thickness on opposite sides of the samepanel. In contradistinction to conventional hot press methods, whatevertemperature gradient exists through the face sheets in the presentmethod operates to maintain a relatively cool exterior surface so thateven with thin face sheets the outer surfaces are not heated to atemperature high enough to produce checking. Any checking under thepresent method is limited to interior surfaces where it is notobjectionable. 'I'he'heat content and face temperatures of a press loadof panels leaving the press is relatively low in comparison withconventional practice, so that the panels may be handled immediatelyupon leaving the press without inconvenience to the workers and withoutdamage to the panels from sudden cooling of platen heated surfaces.

When the core strips within the panel are relatively narrow, such as orstock, the glue may easily be heat set completely through the jointwhile the panel is in the press. When the core members have aconsiderably wider glue line, as for instance, in the case of 2" x 4stock, a cold settingcatalyzed resin glue such as resorcinol, phenolorurea resin may be used. Such glues set quickly when heated and moreslowly at lower temperatures. By heating the glue under time andtemperature conditions sufllcient to-heat setthe glue lines for somedistance in fromthe edges of the joint a suificient bond is quickly.formed to hold the panels together so that they may be handled andremoved from the press without waiting for the interior parts of thejoint to heat set. This partial bond forms an ideal clamp to -hold-thejoint surfaces tightly together and prevent warping of the panel, whilethe rest of the glue continues to set gradually over the wholejointarea.Even after the source of heat is removed there is heat flow into theglue lines from the hot surfaces for some time which progressivelyincreases the width of the marginal heat set bonds'.- The interior partsof the joint th'us' set more slowly until ultimately the wholeare'a'of'the glue line'is completely set, and without the use ofmechanical clamps.

produced by the pistons under the lowerplaten need be sufficient only tolift the pressloa'd of light hollow panels andthen to apply suchadditional pressure as is required to establish the correct unitpressure over the relatively small area of glued surface, the ratio ofthe gluing surface to the total area of the panel being quite small. Thecost of installation of such a press is'much less than that of the usualplywood hot press which is ordinarily used for gluing up hollow panels;Therefore, in virtue of the reduced-heat input, the shortened presstime, and the low initial cost of equipment, the present method effectsa material saving in the over-all cost of production of hollow panels. 1

Although the fluid heating medium has been hereinabove referred to ashot air it is to be understoodthat other gases and vapors havingsuitable thermal conductivity, specific heat, and moisture absorbingproperties may be used, as desired, Having now described my inventionand in what manner the same may be used, what I claim as new and desireto protect by Letters Patent is:

1. The method of heating interior glue joints in a hollow panel to setthe glue without excessively heating the outside faces of the panel,comprising applying external pressure to said outside faces to hold thejoints together, and introducing a heating fluid into the interior ofsaid panel to supply the only source of heat for the panel.

2. The method of heating interior glue joints in hollow panels to setthe glue without excessively heating the outside faces of the panels,comprising pressing the panels between flat unheated surfaces, andintroducing a heating fluid interiorly of the panels.

3. The method of heating interior glue joints in a hollow panel to ahigher temperature than the outside faces of the panel, comprisingapplying external pressure without heat to said outside faces to holdthe joints together, and introducing a heating fluid interiorly of thepanel.

l. The method of heating interior glue joints in a hollow panel to ahigher temperature than the outside faces of the panel, comprisingapplying external pressure without heat to said outside faces to holdthe joints together, and applying heat at substantially atmosphericpressure to the interior surfaces of the panel.

5. The method of heating interior glue joints in a hollow panel to setthe glue without excessively heating the outside faces of the panel,comprising applying external pressure without heat to said outside facesto hold the joints together, introducing a heating fluid interiorly ofthe panel at approximately atmospheric pressure, and discontinuing saidapplication of pressure and introduction of heating fluid when the gluehas set in portions of the joints.

6. The method of heating interior glue joints in hollow panels to setthe glue without excessively heating the outside faces of the panels,comprising pressing a stack of the panels in face to face contact, andpassing hot air through the panels at approximately atmosphericpressure.

7. The method of heating interior glue joints in hollow panels havingapertured ends to set the glue without excessively heating the outsidefaces of the panels, comprising pressing a stack of the panels in faceto face contact, directing a stream of hot air toward one end of thestack, and confining said stream to the endsurface of the stack to causesaid air to flow through the panels.

' 8." Themethod of heating interior glue joints in"hollow=.p'anels withapertured ends to set the glue witho'utexcessively heating the outsidefaces of the-panels,- comprisingpressing a stack of the panels infacetoface contact, applying a heating fluid to'the whole end surface of thestack under sufficient pressure to pass saidheating fluid through thepanels, and removing said heating fluid from the other end of the stack.

1 '9. The method of heating interior glue joints in hollow panels to setthe .glue without excessively heating the outside faces. of the panels,comprising pressinga stack of said panels in faceto face contact,passing a fluid heating medium interiorly through said panels in onedirection-and reversingthe direction of flow of said heating medium fromtime to time to establish a temperature gradient from both ends of saidpanels toward the centers thereof.

' 1.0. The method of heating interior glue joints inhollow panels havingapertured ends to set the glue without excessively heating the outsidefaces of the panels, comprising applyinghot air to the whole end surfaceof a stack of the panels and passing said air through the panels,removing said air from the other end of the stack, applying hot air tothe whole end surfaces of said other end of the stack and passing saidair through the panels in the opposite direction, and reversing said airflow from time to time to establish a temperature gradient from bothends of the panels toward the centers thereof.

11. The method of heating interior glue joints in hollow panels havingapertured ends to set the glue Without excessively heating the outsidefaces of the panels, comprising forming a press load stack of thepanels, confining hot air around the four sides of the stack, passingthe air at one end of said stack through the panels, and removing saidair from the other end of the stack.

12. The method of heating interior glue joints in hollow panels havingapertured ends to set the glue without excessively heating the outsidefaces 0f the panels, comprising pressing a stack of the panels in faceto face contact, passing a heating fluid through said panels to heat theinterior surfaces thereof, and applying a heating fluid to the outeredge surfaces of said panels forming the sides of said stack to heat theedge joints of the panels simultaneously from inside and outside withoutapplying heat to the outer face surfaces of the panels.

13. The method of heating interior glue joints in hollow panels havingapertured ends to set the glue without excessively heating the outsidefaces of the panels, comprising forming a press load stack of saidpanels, heating the ends and sides of said stack with a heating fluid,and passing said heating fluid through said panels alternately inopposite directions.

14. The method of making a glue joint having a glue line with an exposededge comprising applying to the joint surfaces a cold setting resin gluewhich is adapted to set quickly when heated, applying mechanicalpressure to the joint to hold the joint surfaces in intimate contact,applying heat to said exposed edge of the glue line to set quickly theedge portion of the glue line to hold the joint together, thendiscontinuing the application of said heat and pressure before all thelue has set, and allowing the remainder of the glue to set more slowlyat lower temperature without external pressure on the joint; 7

15. Apparatus for gluing hollow rectangular panels having aperturedends, comprising a platen press for pressing a stack of said panelsarranged with the apertured ends of the panels at two opposite ends ofthe stack, hoods defining chambers communicating with said opposite endsof the stack, chambers communicating with the opposite sides of thestack, partitions at the four corners of the stack to separate said endand side chambers, means for passing a heating fluid alternately inopposite directions through said hoods and the interiors of the panels,and means in said side chambers for exteriorly heating the oppositesides of said stack.

16. Apparatus for gluing hollow panels having apertured ends comprisinga cold platen press for pressing a stack of said panels in face to facecontact and arranged with the apertured ends of the panels at twoopposite ends of the stack, a pair of hoods enclosing said opposite endsof the stack respectively when the press is closed, means for passing aheating fluid through said hoods and hollow panels to heat the interiorsurfaces of the panels while the press is 12 closed, and vertical stopsfor the heating fluid engaging opposite sides of the stack and confiningthe heating fluid in said hoods exterior of the stack to the respectiveends of the stack to prevent the passage of heating fluid along thesides of the stack exterior to the panels and compelits passage throughthe interiors of the panels from one hood to the other.

MICHEL PASQUIER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 477,800 Great Britain Jan. 6, 1938

2. THE METHOD OF HEATING INTERIOR GLUD JOINTS IN HOLLOW PANELS TO SETTHE GLUE WITHOUT EXCESSIVELY HEATING THE OUTSIDE FACES OF TE PANELS,COMPRISING PRESSING THE PANELS BETWEEN FLAT UNHEATED SURFACES, ANDINTRODUCING A HEATING FLUID INTERIORLY OF THE PANELS.
 15. APPARATUS FORGLUING HOLLOW RECTANGULAR PANELS HAVING APERTURED ENDS, COMPRISING APLATEN PRESS FOR PRESSING A STACK OF SAID PANELS ARRANGED WITH THEAPERTURED ENDS OF THE PANELS AT TWO OPPOSITE ENDS OF THE STACK, HOODSDEFINING CHAMBERS COMMUNICATING WITH SAID OPPOSITE ENDS OF THE STACK,CHAMBERS COMMUNICATING WITH THE